Biometric authentication systems are used for authenticating users of devices incorporating the authentication systems. Biometric sensing technology provides a reliable, non-intrusive way to verify individual identity for authentication purposes.
Fingerprints, like various other biometric characteristics, are based on unalterable personal characteristics and thus are a reliable mechanism to identify individuals. There are many potential applications for utilization of biometric and fingerprints sensors. For example, electronic fingerprint sensors may be used to provide access control in stationary applications, such as security checkpoints. Electronic fingerprint sensors may also be used to provide access control in portable applications, such as portable computers, personal data assistants (PDAs), cell phones, gaming devices, navigation devices, information appliances, data storage devices, and the like. Accordingly, some applications, in particularly portable applications, may require electronic fingerprint sensing systems that are compact, highly reliable, and inexpensive.
Additionally, in certain applications including an integrated display, a surface area on a front face of the device is a desirable location to provide a biometric sensor, such as a fingerprint sensor. However, locating the fingerprint sensor on the front face of the device can take up additional device real estate that could be used for the display. Alternatively, if the fingerprint sensor is integrated into the active area of the display using conventional techniques, this can interfere with the appearance of the display and distort the image displayed to the user. Furthermore, regardless of any distortion to the appearance of the display, using conventional sensing technologies, it is difficult to reliably sense fine fingerprint features through a thick glass layer or other cover layer that protects most displays.